Solvent extraction process



April 26, 1966 H, F slLVER ETAL 3,248,263

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United States Patent Office 3,248,263 SOLVENT EXTRACTION PROCESS HaroldF. Slver,`Ciarence R. Steele, and Frank B. Price,

Denver, Colo., assignors, by direct and mesne assignments, to AmericanFactors Associates, Limited, Honolulu, Hawaii, a corporation of DelawareFiled Nov. 14, 1962, Ser. No. 237,575 13 Claims. (Cl. 3127-45) Thisinvention relates to a new and improved process for removing orextracting, by the use of a suitable solvent or solvents, solublesubstances from subdivided solids by diffusion, leaching, orlixiviation.

This invention also relates to new and improved apparatus which isespecially adapted for use in carrying out the process of thisinvention.

More specifically, the process and apparatus of this invention aredesigned to carry out the removing and extracting procedure of the typereferred to by a continuous operation, as distinguished from a bathoperation, and to effect such removal or extraction by employing anessentially counter-current liow or movement between the mass ofsubdivided solid material undergoing treatment and the extractingsolvent or solvents employed.

In processes of this type which employ solvent as the liquid extractingmedium it necessarily follows that recovery of the soluble substancefree from the solvent requires subsequent separation of the two, whichis a costly procedure. Accordingly, an objective for an improvement inthis art is that of securing the removal and recovery of the maximumquantity of soluble substance while employing for that purpose thesmallest possible amount of solvent. y Theoretically the counter-currentrelative movement of the solid material and the solvent is well suitedto diffusion, leaching, and lixiviation procedures, and good practicalusage has been made of such practice in the past. However, as far asthese applicants know all prior art procedures of this general typewhich have employed counter-current relative movement between the solidsand solvent to effect such extraction have left a great deal to bedesired from the standpoint of providing a procedure which employs asolids and solvent relationship which adequately approaches the idealfor the most efficient ex- Theoretically, the greatest efficiency wouldbe achieved, other circumstances permitting, if each drop of the liquidsolvent were brought successively into diffusing, leaching, orlixiviating contact with each particle of the solid material, in thatsequence or order establishing a true counter-current flow therebetween.

Whereas such an ideal operation is desirable in principle it poses animpossible problem from the practical standpoint, but, at the same time,it is to be understood that in this art improvement does lie in thedirection of approaching as closely as possible the theoretically idealv3,248,263 Patented Apr. 26, 11966 having substantially uniform bulkdensity and permeability throughout, said mass having its lengthextending horizontally, preferably on the circumference of a circle, buton a straight or other line if desired, its width defined by verticalside faces and its depth maintained at all times at a substantiallyconstant dimension with the upper face thereof constituting asubstantially horizontal even surface disposed at a level which gives tosaid mass a depth dimension of substantial magnitude. It is to beunderstood, however, that the solid material will become slightlycompacted as it travels through the treatment zones, and to this extentthe bulk density and permeability thereof will be slightly altered.

The process of this invention provides for the close lateral confinementof the side faces of said mass without frictional or other disturbance.The apparatus of this invention provides for closely contactingconfining side walls immediately adjacent the side faces of said mass tocontain the solvent placed thereon without relative movement between theside walls and said mass, for confining the solvent to the desireddownward travel throughout said mass without channeling or otherwiseundergoing non-uniform ilow action. The downward flow of the solvent istherefore characterized as being carried out without disturbance ormovement of the material of said mass such as would result from arelative sliding movement between the containing side walls and the massitself. Such relative movement not only would continuously agitate anddisturb the uniform character and disposition of the mass itself, thusproducing channeling or other unwanted actions, but would also disturbthe relatively quiescent downward movement of the solvent in a mannerdetrimental to the high eiiiciency resulting from this invention and, inaddition, would prevent the successful practice of clarificationprocedures, hereinafter more fully explained, contemplated for thisinvention.

The process and apparatus of this invention accordingly provide for thecontinuous application of fresh subdivided solid material at one end ofsaid mass and the continuous removal, at a corresponding rate, of spentsolid material from the other end of said mass, while at all timesmaintaining conditions which will cause the material of said mass to bedeposited in a condition of substantially uniform bulk density andpermeability with a substantially level and even top surface and inclose non-channeling and supported contact with the side walls.

In addition, the process and apparatus of this invention provide for thedesired gravitational passage of the solvent liquid through a limitedand particular zone or portion of the mass so that fresh liquid rstencounters the most spent material and also in such manner that thecontinuous stream of liquid fed to the top of said zone or portion ofsaid mass comes in contact for diffusing, leaching, or lixiviatingactivity with a vertical column of said mass of substantial depth but ofrelatively small cross-sectional area. In addition, the zones oftreatment are determined solely bythe control of the supply of liquidsolvent employed and not by partitions intersecting the mass. In otherwords, this invention provides that the mass from end to end shall becontinuous, uninterrupted, and uniform and thus free of dividing wallsor partitions or any other similar structures such as would createpockets or corners or other spaces that will not uniformly fill asrequired. Thus the continuous character of the mass renders it free fromchanneling or any tendencies which would interfere with the uniformiiow, associa-

1. THE PROCESS OF CONTINUOUSLY EXTRACTING A SOLUBLE SUBSTANCE FROMSUBDIVIDED SOLID MATERIAL WHICH COMPRISES ESTABLISHING AN ELONGATEDSUBSTANTIALLY HORIZONTAL CONTINUOUS MASS OF SAID MATERIAL IN ATROUGH-LIKE UNPARTITIONED RECEPTACLE HAVING A DRAINING BOTTOM ANDUPSTANDING SIDE WALLS OF SUBSTANTIAL HEIGHT, MOVING SAID MASS ANDRECEPTABLE AS A UNIT WHILE PROVIDING CLOSE LATERAL SUPPORT FOR SAID MASSBY SAID SIDE WALLS WITHOUT RELATIVE MOVEMENT BETWEEN SAID MASS AND SIDEWALLS, MAINTAINING SAID MASS BY CONTINUOUSLY ADDING FRESH MATERIAL TOONE END THEREOF AND CONTINUOUSLY REMOVING SPENT MATERIAL FROM THE OTHEREND THEREOF, APPLYING SOLVENT TO THE TOP OF A SELECTED ZONE OF SAID MASSLOCATED ADJACENT THE END THEREOF WHERE THE REMOVAL JOF SPENT MATERIAL ISEFFECTED, CAUS-